From: Jiri Olsa <olsajiri@gmail.com>
To: Ard Biesheuvel <ardb+git@google.com>
Cc: linux-kernel@vger.kernel.org, Ard Biesheuvel <ardb@kernel.org>,
Masahiro Yamada <masahiroy@kernel.org>,
Arnd Bergmann <arnd@arndb.de>,
Martin KaFai Lau <martin.lau@linux.dev>,
linux-arch@vger.kernel.org, linux-kbuild@vger.kernel.org,
bpf@vger.kernel.org, Andrii Nakryiko <andrii@kernel.org>,
Jiri Olsa <olsajiri@gmail.com>
Subject: Re: [PATCH v3 3/3] btf: Avoid weak external references
Date: Mon, 15 Apr 2024 13:22:38 +0200 [thread overview]
Message-ID: <Zh0N_nJKgu43GvYY@krava> (raw)
In-Reply-To: <20240415075837.2349766-8-ardb+git@google.com>
On Mon, Apr 15, 2024 at 09:58:41AM +0200, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel.org>
>
> If the BTF code is enabled in the build configuration, the start/stop
> BTF markers are guaranteed to exist in the final link but not during the
> first linker pass.
>
> Avoid GOT based relocations to these markers in the final executable by
> providing preliminary definitions that will be used by the first linker
> pass, and superseded by the actual definitions in the subsequent ones.
>
> Make the preliminary definitions dependent on CONFIG_DEBUG_INFO_BTF so
> that inadvertent references to this section will trigger a link failure
> if they occur in code that does not honour CONFIG_DEBUG_INFO_BTF.
>
> Note that Clang will notice that taking the address of__start_BTF cannot
> yield NULL any longer, so testing for that condition is no longer
> needed.
>
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
> Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Jiri Olsa <jolsa@kernel.org>
jirka
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
> include/asm-generic/vmlinux.lds.h | 9 +++++++++
> kernel/bpf/btf.c | 7 +++++--
> kernel/bpf/sysfs_btf.c | 6 +++---
> 3 files changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index e8449be62058..4cb3d88449e5 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -456,6 +456,7 @@
> * independent code.
> */
> #define PRELIMINARY_SYMBOL_DEFINITIONS \
> + PRELIMINARY_BTF_DEFINITIONS \
> PROVIDE(kallsyms_addresses = .); \
> PROVIDE(kallsyms_offsets = .); \
> PROVIDE(kallsyms_names = .); \
> @@ -466,6 +467,14 @@
> PROVIDE(kallsyms_markers = .); \
> PROVIDE(kallsyms_seqs_of_names = .);
>
> +#ifdef CONFIG_DEBUG_INFO_BTF
> +#define PRELIMINARY_BTF_DEFINITIONS \
> + PROVIDE(__start_BTF = .); \
> + PROVIDE(__stop_BTF = .);
> +#else
> +#define PRELIMINARY_BTF_DEFINITIONS
> +#endif
> +
> /*
> * Read only Data
> */
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 90c4a32d89ff..6d46cee47ae3 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -5642,8 +5642,8 @@ static struct btf *btf_parse(const union bpf_attr *attr, bpfptr_t uattr, u32 uat
> return ERR_PTR(err);
> }
>
> -extern char __weak __start_BTF[];
> -extern char __weak __stop_BTF[];
> +extern char __start_BTF[];
> +extern char __stop_BTF[];
> extern struct btf *btf_vmlinux;
>
> #define BPF_MAP_TYPE(_id, _ops)
> @@ -5971,6 +5971,9 @@ struct btf *btf_parse_vmlinux(void)
> struct btf *btf = NULL;
> int err;
>
> + if (!IS_ENABLED(CONFIG_DEBUG_INFO_BTF))
> + return ERR_PTR(-ENOENT);
> +
> env = kzalloc(sizeof(*env), GFP_KERNEL | __GFP_NOWARN);
> if (!env)
> return ERR_PTR(-ENOMEM);
> diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
> index ef6911aee3bb..fedb54c94cdb 100644
> --- a/kernel/bpf/sysfs_btf.c
> +++ b/kernel/bpf/sysfs_btf.c
> @@ -9,8 +9,8 @@
> #include <linux/sysfs.h>
>
> /* See scripts/link-vmlinux.sh, gen_btf() func for details */
> -extern char __weak __start_BTF[];
> -extern char __weak __stop_BTF[];
> +extern char __start_BTF[];
> +extern char __stop_BTF[];
>
> static ssize_t
> btf_vmlinux_read(struct file *file, struct kobject *kobj,
> @@ -32,7 +32,7 @@ static int __init btf_vmlinux_init(void)
> {
> bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
>
> - if (!__start_BTF || bin_attr_btf_vmlinux.size == 0)
> + if (bin_attr_btf_vmlinux.size == 0)
> return 0;
>
> btf_kobj = kobject_create_and_add("btf", kernel_kobj);
> --
> 2.44.0.683.g7961c838ac-goog
>
next prev parent reply other threads:[~2024-04-15 11:22 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-15 7:58 [PATCH v3 0/3] kbuild: Avoid weak external linkage where possible Ard Biesheuvel
2024-04-15 7:58 ` [PATCH v3 1/3] kallsyms: Avoid weak references for kallsyms symbols Ard Biesheuvel
2024-04-15 7:58 ` [PATCH v3 2/3] vmlinux: Avoid weak reference to notes section Ard Biesheuvel
2024-04-15 7:58 ` [PATCH v3 3/3] btf: Avoid weak external references Ard Biesheuvel
2024-04-15 11:22 ` Jiri Olsa [this message]
2024-04-15 14:54 ` Masahiro Yamada
2024-04-15 14:59 ` Ard Biesheuvel
2024-04-15 15:31 ` Masahiro Yamada
2024-04-15 15:54 ` Ard Biesheuvel
2024-04-23 11:08 ` [PATCH v3 0/3] kbuild: Avoid weak external linkage where possible Aithal, Srikanth
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